The company's quarterly earnings per share, excluding items, also came in above analysts' expectations as did its quarterly revenue. At the same time, the company gave an upbeat earnings outlook for the current year.

"2012 was a monumental year for Express Scripts as we closed the acquisition of Medco and made significant progress integrating the two companies," stated George Paz, chairman and chief executive officer.

The company's quarterly results were buoyed by its $29 billion acquisition of Medco in April 2012, making it the largest pharmacy benefits manager in the U.S. Pharmacy benefits managers, which act as middlemen for drug makers, pharmacies and health-plan sponsors, are responsible for processing and paying the prescription-drug benefits and claims.

For the fourth quarter ended December 31, 2012, the St. Louis, Missouri based company reported net income of $504.1 million or $0.61 per share, compared to $290.4 million or $0.59 per share for the year-ago quarter.

Income from continuing operations for the fourth quarter was $515.9 million or $0.62 per share, compared to $290.4 million or $0.59 per share in the prior year quarter.

The latest quarter results include amortization of Medco-related intangible assets of $0.35 per share.

Excluding items, adjusted earnings from continuing operations for the fourth quarter were $1.05 per share, compared to $0.82 per share in the fourth quarter of last year.

On average, 21 analysts polled by Thomson Reuters expected the company to earn $1.04 per share for the fourth quarter. Analysts' estimates typically exclude special items.

Revenue for the fourth quarter jumped 127% to $27.41 billion from $12.10 billion in the same quarter last year. Fourteen analysts had a consensus revenue estimate of $27.24 billion for the fourth quarter.

Fourth quarter adjusted claims surged 111% to 410.8 million.

Looking forward, the company forecast 2013 adjusted earnings from continuing operations of $4.20 to $4.30 per share. Analysts currently expect the company to earn $4.20 per share for the full year 2013.

The estimates were reduced from an average of $4.50 per share in November when the company it viewed the then consensus estimate as "overly aggressive".